JP2003218964A - Receiver and error count feedback method employed for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an error count feedback circuit capable of automatically adjusting transmission parameters during operation. <P>SOLUTION: An error count n-second integration section 51 integrates error count values from an error correction circuit 4 for n-seconds. An integration value memory 52 temporarily stores the integrated value, and an adjustment execution discrimination section 53 discriminates ON/OFF of adjustment of a control voltage from the integrated value. A difference circuit 54 calculates a difference between an input at a time (t) and the integrated value before n-seconds, and a voltage adjustment direction decision section 55 decides an adjustment direction of the control voltage from the difference. An adjustment ON/OFF switch 56 outputs the control voltage from the voltage adjustment direction decision section 55 at execution of adjustment and outputs a fixed value in no adjustment state. A control voltage adjustment section 57 obtains a control voltage from a value denoting the voltage adjustment direction and an offset adjustment section 58 adds an offset voltage to the control voltage. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver and an error count feedback method used for the receiver, and more particularly to an error count value indicating the number of errors corrected by an error correction processing unit introduced in a long-distance optical transmission system on a transmission line or in transmission / reception. The present invention relates to a method used as one index indicating the state and characteristics of a machine.

[0002]

2. Description of the Related Art In recent years, error correction processing has been introduced in long-distance optical transmission systems for the purpose of extending the transmission distance, ensuring a system margin, improving the transmission quality, and the like. In general, the error correction processing unit can output an error count value indicating the number of corrected errors in addition to the error correction processing. The error count value is one index indicating the state or characteristics of the transmission line or the transceiver.

Therefore, by controlling various transmission parameters based on the error count information, it becomes possible to adaptively respond to changes in transmission characteristics due to changes in environmental conditions and deterioration of the device over time.

FIG. 12 shows the configuration of a receiver of a general optical transmission system. In the example shown in FIG. 12, after the received optical signal is converted into an electric signal by the O / E (Optical / Electro) converter 1, the clock is regenerated by the clock regenerator 2 and the 0/1 discriminator 3 is used. / 1 is identified, but 0
As the discrimination threshold of / 1, a fixed value is set as shown in FIG. The error correction circuit 4 is a 0/1 identification circuit 3
The error correction process is performed on the 0/1 identification threshold value (data) identified in.

[0005]

However, in the above-mentioned conventional long-distance optical transmission system, as shown in FIG. 13 (b), the signal waveform is changed due to deterioration of the transmission line or receiver or change of environmental conditions. In the case of deterioration, since the 0/1 discrimination point is displaced from the appropriate position, an error is more likely to occur, resulting in deterioration of the characteristics of the receiver.

Therefore, an object of the present invention is to solve the above problems and to provide a receiver capable of automatically adjusting transmission parameters during operation and an error count feedback method used therefor.

[0007]

A receiver according to the present invention comprises:
An error count feedback circuit for a long-distance optical transmission system that uses an error count value indicating the number of errors corrected by an error correction processing unit as one index indicating the state or characteristics of either the transmission path or the transceiver, wherein the error There is provided an adjusting unit that sequentially adjusts the threshold value of the circuit to be controlled using the count value.

Another receiver according to the present invention is a receiver of an optical transmission system including a distribution means for distributing a signal in which a received optical signal is converted into an electric signal, each of which is set to a different bias voltage stepwise. A plurality of amplifying means for amplifying the signals distributed by the distributing means, and a plurality of circuits to be controlled for processing the signals amplified by the plurality of amplifying means.

Another receiver according to the present invention is a receiver of an optical transmission system including a distribution means for distributing a signal obtained by converting a received optical signal into an electric signal, each of which has the same bias voltage and stepwise. A plurality of amplifying means which are set with different gains and amplify the signals distributed by the distributing means,
A plurality of circuits to be controlled, which perform processing on the signals amplified by the plurality of amplifying means.

The error count feedback method according to the present invention uses an error count value indicating the number of errors corrected by the error correction processing unit as one index indicating the state or characteristics of either the transmission line or the transceiver. An error count feedback method for a system, comprising a step of sequentially adjusting a threshold value of a circuit to be controlled using the error count value.

That is, the error count feedback circuit of the present invention is a sequential automatic control using the difference information of the integrated error count value, the suppression of unnecessary adjustment operation by the threshold judgment of the number of errors, and a simple circuit which can be realized by a small circuit. By using a simple logic and memory, it is possible to operate automatically and stably against deterioration of transmission characteristics, and control of transmission parameters during normal operation worsens the characteristics. The danger can be eliminated, and the demand for downsizing the device (the demand for a simple configuration) can be realized.

Further, since the error count feedback circuit of the present invention has a general circuit configuration for error feedback, in addition to the above threshold adjustment for 0/1 discrimination,
It becomes possible to incorporate it into a feedback system that requires an error count value, such as phase adjustment for 0/1 identification, dispersion compensation amount adjustment, and transmission side pre-emphasis amount adjustment.

That is, the control using the error count value requires an error count feedback circuit for generating a control voltage from the error count value. Therefore, in the present invention, the parameters of the transmission line and the receiver are controlled. The proposed error count feedback circuit is proposed.

More specifically, in the error count feedback circuit of the present invention, the threshold value of the 0/1 discriminating circuit is sequentially adjusted by using the error count value from the error correction processing section, whereby the initial state is set. It is possible to keep an appropriate threshold value even when the waveform shifts to the waveform deterioration state.

Further, in the error count feedback circuit of the present invention, besides the example in which the feedback of the error count value is applied to the threshold setting of the discrimination circuit of the receiver, the dispersion compensation amount, the phase of the discrimination circuit, and the pre-emphasis on the transmission side. The automatic adjustment of the amount can be performed in the same manner, and the error count feedback process can be applied to a wide range in the transmission system.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. 1 is a block diagram showing a configuration of a receiver of an optical transmission system according to a first exemplary embodiment of the present invention. In FIG. 1, the optical transmission system according to the first embodiment of the present invention uses an error count value indicating the number of errors corrected by an error correction processing unit to be introduced as one index indicating the state or characteristics of a transmission line or a transceiver. The long-distance optical transmission system used as is shown.

The receiver of the optical transmission system according to the first embodiment of the present invention comprises an O / E (Optical / Electro) converter 1, a clock recovery circuit 2, and a 0/1 identification circuit 3.
And an error correction circuit 4 and an error count feedback circuit 5.

The O / E converter 1 converts the received optical signal into an electric signal, and the clock regeneration circuit 2 regenerates a clock from the electric signal converted by the O / E converter 1. The 0/1 discriminating circuit 3 applies 0/1 to the electrical signal converted by the O / E converter 1 based on the clock reproduced by the clock reproducing circuit 2.
Identify.

The error correction circuit 4 performs error correction processing of the 0/1 identification threshold (data) identified by the 0/1 identification circuit 3 based on the clock reproduced by the clock reproduction circuit 2. The error count feedback circuit 5 outputs the error count value from the error correction circuit 4 to the 0/1 discriminating circuit 3 as a control voltage value, and applies the error count value feedback to the threshold setting of the 0/1 discriminating circuit 3.

FIG. 2A is a diagram showing the relationship between the received waveform at the time of initial setting and the variable threshold in the optical transmission system according to the first embodiment of the present invention, and FIG. 2B is the first embodiment of the present invention. 1
FIG. 6 is a diagram showing a relationship between a reception waveform at the time of deterioration and a variable threshold in the optical transmission system according to the embodiment of

As described above, the error count feedback circuit 5 is configured to successively adjust the threshold value of the 0/1 discriminating circuit 3 using the error count value from the error correction circuit 4, and thus the configuration shown in FIG. From the initial state shown in FIG.
Even if the waveform deteriorates as shown in, it is possible to maintain an appropriate threshold value.

FIG. 3 is a block diagram showing a configuration example of the error count feedback circuit 5 of FIG. In FIG. 3, the error count feedback circuit 5 includes an error count n second integration unit 51, an integrated value memory 52, an adjustment execution determination unit 53, a difference circuit 54, and a voltage adjustment direction determination unit 5.
5, an adjustment ON / OFF switch 56, a control voltage adjustment unit 57, and an offset adjustment unit 58.

The error count value output from the error correction circuit 4 is connected to the input of the error count n-second integration section 51,
The error count n seconds is integrated by the integration unit 51. The integrated value output of the error count n-second integrating section 51 is branched into three, which are respectively input to the integrated value memory 52, the adjustment execution determination section 53, and the difference circuit 54.

The integrated value memory 52 temporarily stores the integrated value of the error count n-second integrating section 51, and its output is connected to the input of the difference circuit 54. The adjustment execution determination unit 53 determines ON / OFF of the control voltage adjustment based on the integrated value of the error count n-second integration unit 51, and the control output is adjusted ON / O.
It is connected to the switch control signal input of the FF switch 56.

The difference circuit 54 calculates the difference between the integrated value of the error count n-second integrating section 51 and the integrated value temporarily stored in the integrated value memory 52, and the difference value output is input to the voltage adjustment direction determining section 55. Connected to. Voltage adjustment direction determination unit 5
Reference numeral 5 determines the adjustment direction of the control voltage from the difference value of the difference circuit 54, and the output of the voltage adjustment direction is connected to the adjustment ON / OFF switch 56.

The adjustment ON / OFF switch 56 selects the voltage adjustment direction output of the voltage adjustment direction determination unit 55 when the adjustment is performed based on the control output of the adjustment execution determination unit 53, and selects the fixed value when the adjustment is not performed. The output is connected to the control voltage adjustment unit 57.

The control voltage adjusting section 57 obtains the control voltage from the value indicating the voltage adjusting direction of the adjustment ON / OFF switch 56, and its output is connected to the input of the offset adjusting section 58. The offset adjusting unit 58 adds an offset voltage (initial value of the control voltage) input from the outside to the control voltage of the control voltage adjusting unit 57, and outputs the final control voltage value as a circuit to be controlled (this embodiment). In the case of, it is output to the 0/1 discrimination circuit 3).

FIG. 4 is a diagram showing an example of a method of determining the voltage adjustment direction V (t) in the optical transmission system according to the first embodiment of the present invention, and FIG. 5 is an optical diagram according to the first embodiment of the present invention. It is a flowchart which shows the voltage adjustment operation | movement in a transmission system. The first aspect of the present invention with reference to FIGS.
A voltage adjustment operation in the optical transmission system according to the embodiment will be described.

The error count feedback circuit 5, based on the error count value output from the error correction circuit 4,
Circuit to be controlled (0/1 discriminating circuit 3 in this embodiment)
It has a function of generating the control voltage of.

First, the error count n-second integration section 51 integrates the error count values from the error correction circuit 4 (FIG. 5).
Steps S1, S2). The error correction circuit 4 outputs an error count value at an error correction processing cycle (generally, several tens of KHz to several tens of MHz).
The second integration unit 51 collects this error count value and integrates it for n seconds. The value of the cumulative number of seconds n is set in consideration of the time interval required by the control target.

Here, the integrated value output at time t is K
(T). Since the value of K (t) is updated every n seconds of the integration interval, t is a multiple of n. The integrated value memory 52 temporarily stores K (t), holds it for n seconds, and then outputs it. Therefore, the integrated value memory 5 at time t
The output of 2 is the integrated value n seconds before (previously processed) with respect to k (t), and can be expressed as K (t-n).

In the difference circuit 54, the input K at time t
The difference between (t) and the integrated value K (t−n) n seconds before is calculated, and the difference value ΔK (t) is output (step S in FIG. 5).
3). That is, ΔK (t) = K (t) −K (t−n).

In the voltage adjustment direction judging section 55, the difference value ΔK
It is determined whether (t) is a positive value or a negative value, and it is determined whether the control voltage is changed to “−ΔV” or “+ ΔV” (step S4 in FIG. 5). Here, ΔV represents the fluctuation range of the control voltage and is set according to the adjustment accuracy of the control target. When the error is “0” and the difference value is “0”, the fluctuation range is set to “0”.

The control voltage adjustment direction at time t is V
If (t), V (t) is “−ΔV”, “+ ΔV”,
It is one of the three values "0". The voltage adjustment direction is shown in Fig. 4.
As shown in, when the difference value ΔK (t) is positive, the adjustment direction of the previous time (n seconds ago) is reversed, and the difference value ΔK (t) is changed.
If is negative, the previous adjustment direction (n seconds ago) is maintained as it is (step S5 in FIG. 5).

That is, as a result of adjusting the control voltage in a certain direction n seconds before, if the error increases, the adjustment direction is switched to the opposite direction, and if the error decreases, the direction is maintained as it is. , Make the control voltage converge to an appropriate value.

When V (t-n) of the previous time (n seconds before) is "0", the difference value ΔK (t) is temporarily adjusted in the "+ ΔV" direction regardless of whether it is positive or negative. The adjustment ON / OFF switch 56 at the next stage turns ON when the adjustment is performed,
V (t) from the voltage adjustment direction determination unit 55 is input to the control voltage adjustment unit 57, but is turned off when not adjusted, and a fixed value of V (t) = 0 is input to the control voltage adjustment unit 57.
Adjustment of the control voltage is suppressed. The adjustment execution determination unit 53 determines whether the adjustment is ON or OFF.

The error integrated value K (t) at time t is constantly monitored, and when the error integrated value exceeds the set threshold value A, the voltage adjustment is turned on. If the number of errors falls below the threshold value B as a result of continuing the voltage adjustment, the voltage adjustment is turned off again.
Let it be F.

The control voltage adjusting unit 57 obtains the control voltage Vs' (t) from V (t) indicating the voltage adjusting direction (step S6 in FIG. 5). The control voltage Vs ′ (t) is Vs ′ (t) = Vs ′ (t−n) + V (t), and the control voltage is obtained by sequentially adding V (t) output every n seconds. The initial value of Vs' (t) is "0".

The offset voltage α input to the offset adjusting section 58 at the final stage is set in the initial stage so that the control voltage becomes optimum for the controlled object. The final control voltage output Vs (t) to the controlled object is Vs (t) = Vs ′ (t) + α. In the control target, the parameter is changed according to the output of Vs (t) that is sequentially updated from the initial value α of the control voltage (steps S7 and S8 in FIG. 5).

That is, in the error count feedback circuit 5, when the error integrated value increases for some reason and exceeds the threshold value A, adjustment of the control voltage Vs (t) is started. The control voltage Vs (t) is continuously adjusted every n seconds, the parameter of the control target is changed accordingly, and as a result, the error count value changes.

When the adjustment of the control voltage Vs (t) progresses and approaches an appropriate value, the error integrated value decreases and the adjustment of the control voltage Vs (t) is suppressed at the time when it falls below the threshold value B.
The threshold A for adjustment start determination and the threshold B for adjustment stop determination are A
A hysteresis is provided as a relation of> B to stabilize the switching operation. Error count feedback circuit 5
By sequentially repeating this operation, the control voltage Vs (t) for the controlled object can be maintained at an appropriate value.

As described above, in this embodiment, the transmission parameters during operation can be automatically adjusted by performing the sequential control using the difference information of the integrated error count value. Further, since the configuration of the present embodiment can be configured by simple logic and memory, it can be realized by a small-scale circuit, and the mounted device can be downsized.

Further, since the present embodiment has a general circuit configuration for error count feedback, the error count value such as the threshold adjustment for 0/1 identification, the phase adjustment, the dispersion compensation amount adjustment and the transmission side pre-emphasis amount adjustment is performed. Can be universally incorporated into a transmission line parameter adjustment feedback system requiring.

FIG. 6 is a block diagram showing a configuration example of an error count feedback circuit according to the second embodiment of the present invention. In FIG. 6, the error count feedback circuit 6 outputs the control output of the adjustment execution determination unit 61 to the difference circuit 54.
Adjustment ON / OFF by connecting to the reset input of
The first aspect of the present invention shown in FIG. 3 except that the switch 56 is removed.
The configuration is similar to that of the error count feedback circuit 5 according to the embodiment, and the same components are designated by the same reference numerals. The operation of the same component is the first aspect of the present invention.
It is similar to the embodiment of.

When the adjustment execution determination unit 61 determines that the adjustment is ON, it does not issue a reset signal and performs the same operation as that of the embodiment of the present invention. When the adjustment execution determination unit 61 determines that the adjustment is OFF, the output of the difference circuit 54 is reset and Δ
Fix K (t) = 0.

As shown in FIG. 4, when ΔK (t) = 0, the output V (t) of the voltage adjustment direction determination unit 85 is also “0”.
Therefore, as a result, the control voltages Vs ′ (t) and Vs
(T) is not adjusted. Therefore, the second embodiment of the present invention enables the same operation as that of the first embodiment of the present invention shown in FIG.

FIG. 7 is a block diagram showing a configuration example of an error count feedback circuit according to the third embodiment of the present invention. 7, the error count feedback circuit 7 has the same configuration as the error count feedback circuit 5 according to the first embodiment of the present invention shown in FIG. 3 except that the adjustment execution determination unit 51 and the adjustment ON / OFF switch 56 are deleted. The same constituent elements are designated by the same reference numerals. The operation of the same component is the same as that of the first embodiment of the present invention.

In the third embodiment of the present invention, the ON / OFF of the adjustment based on the threshold judgment of the error integrated value is not performed, and only the output ΔK (t) of the difference circuit 54 is used as the adjustment condition for the control voltage Vs' (t). , Vs (t) are adjusted.

When an error occurs and ΔK (t) ≠ 0, the same operation as that of the first embodiment of the present invention shown in FIG. 3 is performed. Further, when the control voltage Vs (t) is adjusted to an appropriate value and there is no error, both the error count value K (t) and the integrated value K (t−n) before n seconds become “0”. , ΔK (t) = 0.

As shown in FIG. 4, when ΔK (t) = 0, the output V (t) of the voltage adjustment direction determination unit 55 also becomes “0”, and as a result, the control voltage Vs ′ (t). And Vs
(T) is not adjusted. Therefore, the third embodiment of the present invention enables the same operation as that of the first embodiment of the present invention shown in FIG.

FIG. 8 is a block diagram showing the configuration of the receiver of the optical transmission system according to the fourth embodiment of the present invention.
FIG. 9 is a diagram showing a relationship between a received waveform and a threshold value in the optical transmission system according to the fourth example of the present invention.

In FIG. 8, the receiver 8 includes an O / E converter 81, a distributor 82, and amplifiers 83-1 to 83- (2.
^n- 1) and high-speed binary decision circuits 84-1 to 84- ( ²ⁿ
-1) and is connected to the FEC circuit 9.

In the above-described first to third embodiments of the present invention, the output of the O / E converter 1 is branched by a distributor (not shown) and directly input to the 0/1 discriminating circuit 3. However, there are many cases in which a signal is amplified by using an amplifier after the O / E conversion processing, and in these cases, as shown in FIG.
Even in the conventional configuration as shown in FIG.
The same effect as the third embodiment can be obtained.

In this embodiment, an amplifier and a high-speed binary decision circuit are provided by the number 2 ⁿ -1 of thresholds required for n-bit soft decision, and these amplifiers 83-1 to 83- (2 ⁿ -1)
And high-speed binary decision circuits 84-1 to 84- (2 ⁿ -1) are connected in parallel.

High speed binary decision circuits 84-1 to 84- (2 ⁿ
All the thresholds of -1) are fixed to the same value of α ',
Bias voltage B of the amplifiers 83-1 to 83- (2 ⁿ -1)
ias_1 to Bias_2 ⁿ -1 are set to different values stepwise.

In the case of this embodiment, the received waveform and the discrimination threshold α '
The relationship with is as shown in FIG. 9, and the fixed discrimination threshold α ′
Since the level of the received signal rises and falls with respect to the level of, the same effect as that of the above-described first to third embodiments of the present invention can be obtained.

FIG. 10 is a block diagram showing the configuration of the receiver of the optical transmission system according to the fifth embodiment of the present invention, and FIG. 11 is the received waveform and threshold in the optical transmission system according to the fifth embodiment of the present invention. It is a figure which shows the relationship with.

[0058] In FIG. 10, fifth receiver 10 according to an embodiment of the present invention, the amplifier 91-1~91- (2 ⁿ -
Each bias voltage of 1) is fixed and each gain G
The configuration is the same as that of the receiver 8 according to the fourth exemplary embodiment of the present invention shown in FIG. 8 except that ain_1 to Gain_2 ⁿ -1 are set stepwise, and the same reference numerals are given to the same components. It is attached. The operation of the same components is the same as that of the fourth embodiment of the present invention.

In the case of this embodiment, the received waveform and the discrimination threshold α '
11 is shown in FIG. 11, and the level of the received signal is different from that of each amplifier 91 with respect to the level of the fixed identification threshold value α ′.
-1 to 91- (2 ⁿ -1) gains Gain_1 to Ga
Since it varies depending on the difference of in — 2 ⁿ −1, the same effect as that of the above-described first to third embodiments of the present invention can be obtained equivalently.

[0060]

As described above, the present invention uses the error count value indicating the number of errors corrected by the error correction processing unit as one index indicating the state or characteristics of either the transmission line or the transceiver. In the optical transmission system, by successively adjusting the threshold value of the circuit to be controlled using the error count value, it is possible to obtain the effect that the transmission parameters can be automatically adjusted during operation.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a receiver of an optical transmission system according to a first exemplary embodiment of the present invention.

FIG. 2A is a diagram showing a relationship between a reception waveform at initial setting and a variable threshold in the optical transmission system according to the first embodiment of the present invention, and FIG. 2B is according to the first embodiment of the present invention. It is a figure which shows the relationship between the received waveform at the time of deterioration in an optical transmission system, and a variable threshold value.

FIG. 3 is a block diagram showing a configuration example of an error count feedback circuit of FIG.

FIG. 4 is a diagram showing an example of a method for determining a voltage adjustment direction in the optical transmission system according to the first embodiment of the present invention.

FIG. 5 is a flowchart showing a voltage adjusting operation in the optical transmission system according to the first embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration example of an error count feedback circuit according to a second embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration example of an error count feedback circuit according to a third embodiment of the present invention.

FIG. 8 is a block diagram showing a configuration of a receiver of an optical transmission system according to a fourth exemplary embodiment of the present invention.

FIG. 9 is a diagram showing a relationship between a received waveform and a threshold value in the optical transmission system according to the fourth example of the present invention.

FIG. 10 is a block diagram showing a configuration of a receiver of an optical transmission system according to a fifth exemplary embodiment of the present invention.

FIG. 11 is a diagram showing a relationship between a received waveform and a threshold value in the optical transmission system according to the fifth example of the present invention.

FIG. 12 is a block diagram showing a configuration of a receiver of a conventional optical transmission system.

FIG. 13A is a diagram showing a relationship between a reception waveform at the time of initial setting and a fixed threshold in the optical transmission system according to the conventional example,
(B) is a diagram showing a relationship between a reception waveform and a fixed threshold value at the time of deterioration in the optical transmission system according to the conventional example.

[Explanation of symbols]

1 O / E conversion unit 2 Clock recovery circuit 3 0/1 identification circuit 4 Error correction circuit 5 to 7 Error count feedback circuit 51 Error count n second integration unit 52 Integrated value memory 53, 61 Adjustment execution determination unit 54 Difference circuit 55 Voltage Adjustment direction determination unit 56 Adjustment ON / OFF switch 57 Control voltage adjustment unit 58 Offset adjustment unit 8 and 10 Receiver 81 O / E converter 82 Distributors 83-1 to 83- (2 ⁿ -1), 91-1 to 91 -(2 ⁿ -1) amplifiers 84-1 to 84- (2 ⁿ -1) high speed binary decision circuit

Claims (10)

[Claims] 1. A receiver of an optical transmission system, wherein an error count value indicating the number of errors corrected by an error correction processing unit is used as one index indicating the state or characteristics of either the transmission path or the transceiver, wherein: A receiver comprising an adjusting unit that sequentially adjusts a threshold value of a circuit to be controlled using an error count value. 2. The adjusting means integrates the error count values from the error correction section, an integrated value memory for temporarily storing the integrated value of the integrating means, and an integrated value of the integrating means. Difference calculating means for calculating a difference from the integrated value stored in the integrated value memory, and voltage adjusting direction determining means for determining the adjusting direction of the control voltage to the circuit to be controlled from the difference value of the difference calculating means. A control voltage adjusting means for obtaining a control voltage from the determination result of the voltage adjusting direction determining means, and an offset voltage input from the outside to the control voltage obtained by the control voltage adjusting means, and output to the circuit to be controlled. 2. The receiver according to claim 1, further comprising offset adjusting means for performing the adjustment. 3. A judgment means for judging whether or not the control voltage is adjusted based on the integrated value of the integration means, and a voltage adjustment direction output of the voltage adjustment direction judgment means is selected when the judgment result of the judgment means indicates that the adjustment is performed. The adjusting means includes switch means for selecting a preset fixed value when the judgment result of the judging means is not adjusted.
The receiver described. 4. A judgment means for judging whether or not the control voltage is adjusted based on the integrated value of the integrating means, and a preset value set by resetting the output of the difference means when the judgment result of the judging means is not adjusted. 3. The receiver according to claim 2, wherein the adjusting means includes means for outputting a fixed value. 5. A receiver of an optical transmission system including a distribution means for distributing a signal obtained by converting a received optical signal into an electric signal, wherein the receivers are set to different bias voltages stepwise and distributed by the distribution means. A receiver comprising: a plurality of amplifying means for amplifying the amplified signal; and a plurality of control target circuits for processing the signals amplified by the plurality of amplifying means. 6. A receiver of an optical transmission system including a distributing means for distributing a signal obtained by converting an optical signal received into an electric signal, wherein the same bias voltage and stepwise different gains are set, respectively. A receiver comprising: a plurality of amplifying means for amplifying the signal distributed by the distributing means; and a plurality of circuits to be controlled for processing the signals amplified by the plurality of amplifying means. 7. An error count feedback method for an optical transmission system, wherein an error count value indicating the number of errors corrected by an error correction processing unit is used as one index indicating the state or characteristics of either the transmission path or the transceiver. An error count feedback method comprising the step of sequentially adjusting a threshold value of a circuit to be controlled using the error count value. 8. The step of sequentially adjusting the threshold value includes a step of integrating error count values from the error correction section, a step of temporarily storing the integrated value in an integrated value memory, the integrated value and the A step of calculating a difference from the integrated value stored in the integrated value memory, a step of determining the adjustment direction of the control voltage to the circuit to be controlled from the difference value, and a step of obtaining a control voltage from the determination result. 8. The error count feedback method according to claim 7, further comprising a step of adding an offset voltage input from the outside to the obtained control voltage and outputting the control voltage to the circuit to be controlled. 9. The step of sequentially adjusting the threshold value includes a step of determining whether or not the control voltage is adjusted from the integrated value, and a voltage adjustment direction output of the voltage adjustment direction determination means when the result of the determination is adjustment. And selecting a preset fixed value when the judgment result is unadjusted. 10. The step of sequentially adjusting the threshold comprises:
It is characterized by including a step of judging whether or not the control voltage is adjusted from the integrated value, and a step of resetting the difference value and outputting a preset fixed value when the judgment result is not adjusted. The error count feedback method according to claim 8.